A placebo effect is a psychological phenomenon, in which the recipient perceives an improvement in condition due to personal expectations, rather than the treatment itself. Generally speaking, the more serious the treatment, the higher the extent of the placebo effect. For example, the placebo effect from a ‘fake’ cream will likely be less than from a ‘fake’ pill, which will likely be less than from a ‘fake’ surgery.
The only way to discern whether or not an improvement of a specific condition from a specific treatment is due to a placebo effect is through clinical research. There is no other way of knowing whether or not the effectiveness of treatment (including Reiki) is due to a placebo effect.
Personally, I have a lot of experience with Reiki and based on my observational experience, I am certain that the effectiveness of Reiki is significantly above the placebo effect (and trust me, as a medical doctor and a clinical research physician I approach Reiki with a critical eye, just as I do any other type of treatment).
Unfortunately, in spite of numerous studies on the effectiveness of Reiki, there is no definitive proof that it it is helpful beyond a placebo effect. For the most part, this is due to research of inadequate quality. To quote the analysis of multiple studies on Reiki by Sondra vanderVaart et. al (Mary Ann Liebert, Inc.):
“The serious methodological and reporting limitations of limited existing Reiki studies preclude a definitive conclusion on its effectiveness. High-quality randomized controlled trials are needed to address the effectiveness of Reiki over placebo.”
It is not surprising, since most researchers are not Reiki practitioners and most Reiki practitioners are not researchers. How can you study something you know very little about, and how can you create a high quality clinical trial on something you know a lot about if you don’t know anything about research?
Just because the clinical research data is limited, it does not mean that the effectiveness of Reiki comes purely from a placebo effect. I have no doubt, that with high quality studies, we will be able to demonstrate clinically significant difference between the effectiveness of Reiki for a wide range of indication vs. placebo. It is simply a question of time and high quality studies.